Beyond Simple AGN Unification with Chandra-observed 3CRR Sources at 0.5 < z < 1

Low-frequency radio selection finds radio-bright galaxies regardless of the amount of obscuration by gas and dust. We report Chandra observations of a complete 178 MHz-selected, and so orientation unbiased, sample of 44 0.5 < z < 1 3CRR sources. The sample is comprised of quasars and narrow-line radio galaxies (NLRGs) with similar radio luminosities, and the radio structure serves as both an age and an orientation indicator. Consistent with Unification, intrinsic obscuration (measured by NH, X-ray hardness ratio, and X-ray luminosity) generally increases with inclination. However, the sample includes a population not seen in high-z 3CRR sources: NLRGs viewed at intermediate inclination angles with NH < 1022 cm−2. Multiwavelength analysis suggests these objects have lower L/LEdd than typical NLRGs at similar orientation. Thus both orientation and L/LEdd are important, and a “radiation-regulated Unification” provides a better explanation of the sample’s observed properties. In comparison with the 3CRR sample at 1 < z < 2, our lower-redshift sample shows a higher fraction of Compton-thin NLRGs (45% vs. 29%) but similar Compton-thick fraction (20%), implying a larger covering factor of Compton-thin material at intermediate viewing angles and so a more “puffed-up” torus atmosphere. We posit that this is due to a range of L/LEdd extending to lower values in this sample. In contrast, at high redshifts the narrower range and high L/LEdd values allowed orientation (and so simple Unification) to dominate the sample’s observed properties.